Water-soluble metalworking fluid, and metalworking coolant

ABSTRACT

A water-soluble metalworking fluid of the invention contains: a component (A) that is a dicarboxylic acid including a sulfide structure; a component (B) that is a polyalkylene glycol; a component (C) that is polyhydric alcohol polyalkylene oxide adducts; and a component (D) that is a monocarboxylic acid.

TECHNICAL FIELD

The present invention relates to a water-soluble metalworking fluid anda metalworking coolant provided by diluting the fluid with water.

BACKGROUND ART

A metalworking fluid used in metalworking is generally categorized intooil-type (oil-based) fluid and water-type (water-based) fluid, thelatter of which is more frequently used because such water-based fluidis excellent in cooling capabilities and penetration capabilities andfree from a risk of causing a fire.

Particularly, since cooling capabilities of the fluid is significant ingrinding, a solution-type fluid not containing a mineral oil isfrequently used (see, for instance, Patent Literature 1). Thesolution-type fluid exhibits favorable cooling capabilities and rotresistance, but exhibits inferior lubricity to those of non-water-type,emulsion-type and soluble-type fluids. An insufficient lubricity causesdeterioration in roughness of a machined surface, a decrease in lifetimeof a grinding stone, or grinding burn.

Accordingly, in order to add the lubricity to the soluble-type fluid,polyalkylene glycol (PAG) is sometimes blended with the fluid (seePatent Literatures 2 and 3).

CITATION LIST Patent Literature(s)

Patent Literature 1: JP-A-40-14480

Patent Literature 2: JP-A-10-324888

Patent Literature 3: JP-A-2010-70736

SUMMARY OF THE INVENTION Problem(s) To Be Solved By The Invention

In the soluble-type fluids disclosed in Patent Literatures 2 and 3, afavorable lubricity is obtained by increasing an amount of PAG. However,even if a great amount of PAG is blended, improvement in the lubricityis limited. Accordingly, under severe machining conditions, a frictioncoefficient between a grinding stone and a ground material is increasedto cause a decrease in lifetime of the grinding stone and grinding burn.

An object of the invention is to provide a water-soluble metalworkingfluid exhibiting excellent lubricity and wear resistance even undersevere machining conditions, and a metalworking coolant provided bydiluting the water-soluble metalworking fluid with water.

Means For Solving The Problem(s)

The inventors found that the lubricity and the wear resistance could beimproved by using a water soluble fluid containing all of a dicarboxylicacid having a sulfide structure, PAG, a polyalkylene oxide adduct ofpolyhydric alcohol such as pentaerythritol, and a monocarboxylic acid.The invention has been reached based on this finding.

Specifically, the invention provides a water-based metalworking fluidand a metalworking coolant as follows.

According to an aspect of the invention, a water-soluble metalworkingfluid includes: a component (A) that is a dicarboxylic acid comprising asulfide structure; a component (B) that is a polyalkylene glycol; acomponent (C) that is polyhydric alcohol polyalkylene oxide adducts; anda component (D) that is a monocarboxylic acid.

According to another aspect of the invention, a water-solublemetalworking coolant is provided by diluting the above-mentionedwater-soluble metalworking fluid with water by 2 to 200 times in volume.

The water-soluble metalworking fluid (undiluted solution) of theinvention exhibits favorable lubricity and wear resistance in a form ofa metalworking coolant provided by diluting the fluid with water.Accordingly, when the metalworking coolant of the invention is used forgrinding, the metalworking coolant is unlikely to cause deterioration inroughness of a machined surface even under severe machining conditions,so that grinding burn and a decrease in lifetime of the grinding stonecan be sufficiently restrained.

DESCRIPTION OF EMBODIMENT(S)

A water-soluble metalworking fluid according to an aspect of theinvention (hereinafter, also referred to as “the present fluid”) isprovided by blending: a component (A) that is a dicarboxylic acidcomprising a sulfide structure; a component (B) that is a polyalkyleneglycol; a component (C) that is polyhydric alcohol polyalkylene oxideadducts; and a component (D) that is a monocarboxylic acid. The presentfluid is an undiluted solution and is diluted with water to provide ametalworking coolant according to another aspect of the invention. Thepresent invention will be described in detail below.

Component (A)

A component (A) of the present fluid is a dicarboxylic acid including asulfide structure and has an effect of improving lubricity.

As the component (A), a dicarboxylic acid represented by a formula (1)below is particularly excellent in improvement in lubricity.

HOOC—R¹—S_(n)—R²—COOH   (1)

Herein, R¹ and R² each are a hydrocarbon group having 1 to 5 carbonatoms. n is an integer from 1 to 8. When R¹ and R² each contain 6 ormore carbon atoms, water solubility may be deteriorated.

The total number of the carbon atoms in the dicarboxylic acid of theformula (1) is in a range from 4 to 12, however, is preferably in arange from 6 to 10 in terms of water solubility and lubricity. R¹ and R²each are preferably an alkylene group, examples of which include amethylene group, ethylene group, methyl ethylene group, propylene group,and butylene group. An ethylene group is particularly preferable interms of water solubility and lubricity.

When n is 9 or more, the dicarboxylic acid becomes structurally unstableand may be decomposed. Accordingly, n is preferably 6 or less, morepreferably 2 or less, further preferably 1.

Examples of the dicarboxylic acid include thiodipropionic acid,dithiodipropionic acid, thiodiacetate, thiodisuccinate, dithiodiacetate,and dithiodibutyrate.

A content of the component (A) is preferably in a range from 0.1 mass %to 14 mass % based on the total amount of the undiluted solution, morepreferably from 1 mass % to 10 mass %, further preferably from 2 mass %to 5 mass %. When the content of the component (A) is excessively large,rust resistance of the present fluid (undiluted solution) diluted withwater may be decreased.

Component (B)

A component (B) of the present fluid, which is polyalkylene glycol,contributes to improvement in lubricity in the same manner as thecomponent (A) and further contributes to improvement in wear resistance.The component (B) is preferably at least one of polyalkylene glycolrepresented by formulae (2) and (3) below in terms of improvement inlubricity and wear resistance.

HO—(EO)a-(PO)b-(EO)c-H   (2)

R³O—(R′O)d-H   (3)

In the formula (2), EO denotes an ethylene oxide unit and PO denotes apropylene oxide unit. a and c each independently are an integer from 1to 30. b is an integer from 5 to 100. The total number of an EOstructure in the formula (2) is preferably in a range from 10 to 30. Thetotal number of a PO structure in the formula (2) is preferably in arange from 10 to 50, more preferably in a range from 20 to 40. When thetotal number of the EO structure exceeds 60, lubricity of the presentfluid diluted with water may be decreased. When the total number of thePO structure exceeds 100, water solubility may be decreased.

In the formula (3), R³ is an alkyl group having 1 to 30 carbon atoms.When the number of the carbon atoms in R³ exceeds 30, water solubilitymay be decreased. R′O denotes an oxide unit selected from PO and EO. Amixture of PO and EO may be used in R′O. It should be noted that a molefraction of EO in R′O is preferably less than 1 in terms of antifoamingproperty of the present fluid diluted with water. d is an integer from 1to 50. When the number of the carbon atoms in R³ exceeds 30, watersolubility may be decreased.

A mass average molecular weight of the component (B) is preferably 500to 10000, more preferably 1000 to 5000. When the mass average molecularweight is less than 500 or more than 10000, lubricity of the presentfluid diluted with water may be decreased.

Polyalkylene glycol represented by the formulae (2) and (3) that is thecomponent (B) may be used alone or in a mixture. Moreover, polyalkyleneglycol represented by the formulae (2) and (3) may be in a mixture ofpolyalkylene glycol having various structures that are different in, forinstance, the number of the units of the EO structure and PO structure.

A content of the component (B) is preferably in a range from 10 mass %to 60 mass % based on the total amount of the undiluted solution, morepreferably from 20 mass % to 40 mass %, further preferably from 20 mass% to 30 mass %. When the content of the component (B) is excessivelylarge, lubricity after being diluted at a typical dilution ratio may beexcessively increased to decrease a biting performance of a grindingstone in grinding.

Component (C)

A component (C) of the present fluid is at least one of the compoundsrepresented by the formulae (4) to (7). The component (C) contributes toimprovement in wear resistance.

In the formula (4), R¹¹ to R¹⁴ are each independently an alkylene grouphaving 1 to 5 carbon atoms. e to h are each independently an integerfrom 1 to 30.

In the formula (5), R⁴ is an alkyl group having 1 to 30 carbon atoms.R²¹ to R²³ are each independently an alkylene group having 1 to 5 carbonatoms. i to k are each independently an integer from 1 to 30.

In the formula (6), R⁵ and R⁶ are each independently an alkyl grouphaving 1 to 30 carbon atoms. R³¹ and R³² are each independently analkylene group having 1 to 5 carbon atoms. 1 to m are each independentlyan integer from 1 to 30.

In the formula (7), R⁷ to R⁹ are each independently an alkyl grouphaving 1 to 30 carbon atoms. R⁴¹ is an alkylene group having 1 to 5carbon atoms. n is an integer from 1 to 30.

Among the above component (C), an EO adduct of pentaerythritol or an EOadduct of trimethylolpropane is preferable in terms of improvement inwear resistance.

A content of the component (C) is preferably in a range from 5 mass % to30 mass % of the total amount of the present fluid in terms of wearresistance at a typical dilution ratio.

Component (D)

A component (D) of the present fluid, which is a monocarboxylic acid,contributes to improvement in lubricity and wear resistance. Themonocarboxylic acid is preferably a so-called long-chain carboxylicacid, specifically a compound represented by a formula (8) below.

R¹⁰—COOH   (8)

R¹⁰ is a hydrocarbon group having 11 or more carbon atoms. Thehydrocarbon group may be linear or branched and saturated orunsaturated. Tall oil fatty acid is preferable in terms of lubricity andwear resistance.

Specific examples of the long-chain carboxylic acid include lauric acid,stearic acid, oleic acid, linolic acid, linolenic acid, erucic acid,palmitic acid, ricinoleic acid, hydroxy fatty acid (e.g., ricinoleicacid, 12-hydroxystearic acid), arachidic acid, behenic acid, melissicacid, isostearic acid, soy oil fatty acid extracted from fat and oil,coconut oil fatty acid, rape-seed oil fatty acid, and tall oil fattyacid (C18).

A content of the component (D) is preferably in a range from 1 mass % to20 mass % of the total amount of the present fluid in terms of lubricityand wear resistance at a typical dilution ratio.

The present fluid is provided in a form of the undiluted solutionobtained by blending the above components (A) to (D) with water. In thepresent fluid (undiluted solution), a total content of the components(A) to (D) is preferably in a range from 40 mass % to 90 mass % of thetotal amount of the present fluid, more preferably from 60 mass % to 80mass %.

When the total content of the components (A) to (D) is less than 40 mass%, a decrease in lubricity (an increase in a friction coefficient) mayoccur if the present fluid is diluted with water at an excessively highdilution ratio at a working site. On the other hand, when the totalcontent of the components (A) to (D) exceeds 90 mass %, stability of theundiluted solution may be decreased. The stability of the undilutedsolution means that uniformity of the undiluted solution is lost due tophase separation, undissolved mass or precipitation of solid content andthe like.

Water for preparing the undiluted solution is preferably 15 mass % to 75mass % of the total amount of the present fluid. When water is less than15 mass %, dissolution of the components (A) and (B) becomes difficultand preparation of the undiluted solution becomes complicated. Whenwater for preparing the undiluted solution exceeds 75 mass %, anexcessive amount of the undiluted solution has to be stored ortransported, thereby lowering handleability.

The fluid (undiluted solution) may be directly used, but, is preferablydiluted with water at a ratio (volume ratio) of 2 to 200 times,preferably 5 to 100 times to be used as a metalworking coolant.

Other Components

It is preferable that the present fluid further contains a nonion-basedsurfactant as a component (E). By blending such a surfactant,wettability of the present fluid is improved, so that the present fluideasily penetrates between the grinding stone and a ground material.

An acethylene glycol surfactant is particularly preferable as thecomponent (E) in terms of the effects. As the acethylene glycolsurfactant, for instance, acethylene glycol and an alkylene oxide adductthereof disclosed in JP-A-2011-12249 are suitably usable. For instance,an acethylene glycol EO adduct is suitable. Examples of a commerciallyavailable acethylene glycol surfactant include Dynol 604, Surfynol 420and Surfynol 465 which are manufactured by Air Products and Chemicals,Inc.

A content of the component (E) is preferably in a range from 0.1 mass %to 20 mass % of the total amount of the undiluted solution, morepreferably from 1 mass % to 10 mass %. When the content of the component(E) is excessively large, antifoaming performance of the present fluidafter being diluted is deteriorated.

It is preferable that the present fluid further contains alkanolamine asa component (F). Alkanolamine reacts with the component (A) or thecomponent (D) to form alkanolamine carboxylate, thereby improvinglubricity. Moreover, alkanolamine also serves as a rust inhibitor.

The kind of alkanolamine is not particularly limited. A combination ofprimary, secondary and tertiary amines is usable. However, when only theprimary amine is used, since volatility of the primary amine is high,working environments may be deteriorated because of odor generation.Accordingly, when the primary amine is used, it is preferable to combinethe secondary amine and/or tertiary amine with the primary amine. Thetertiary amine is preferable in terms of odor generation.

Examples of the primary amine are 1-amino-2-propanol,2-amino-2-methyl-1-propanol, 1-amino-2-butanol, 2-amino-1-propanol, and3-amino-2-butanol. Among the above, in view of the rust resistance foriron, 1-amino-2-propanol and 2-amino-2-methyl-1-propanol areparticularly preferable. In the present fluid, one of the abovecomponents may be used alone, or two or more thereof may be used.

Examples of the secondary amine include diethanolamine,di(n-propanol)amine, diisopropanolamine, N-methylmonoethanolamine,N-ethylmonoethanolamine, N-cyclomonoethanolamine,N-n-propylmonoethanolamine, N-i-propylmonoethanol amine,N-n-butylmonoethanol amine, N-i-butylmonoethanolamine, andN-t-butylmonoethanolamine. In the present fluid, one of the abovecomponents may be used alone, or two or more thereof may be used.

Examples of the tertiary amine include N-methyldiethanolamine,N-ethyldiethanolamine, triethanolamine, N-cyclohexyldiethanol amine,N-n-propyldiethanolamine, N-i-propyldiethanolamine,N-n-butyldiethanolamine, N-i-butyldiethanolamine, andN-t-butyldiethanolamine. One of the above components may be used alone,or two or more thereof may be used.

A content of the component (F) is preferably in a range from 20 mass %to 55 mass % of the total amount of the present fluid (undilutedsolution). When the content of the component (F) is less than 20 mass %,rust resistance may be decreased if the present fluid is diluted withwater at an excessively high dilution ratio at a working site. On theother hand, when the content of the component (F) exceeds 55 mass %, thestability of the undiluted solution is lowered.

Herein, in order to improve the rust resistance, it is preferable to usecarboxylic acid containing no sulfur as the rust inhibitor together withthe component (F). In view of antifoaming capabilities and hard waterstability, preferable examples of the carboxylic acid include: amonocarboxylic acid such as caproic acid, nonane acid, isononane acid,trimethylhexanoic acid, neodecanoic acid and decane acid having 8 to 10carbon atoms; and a dicarboxylic acid such as nonane diacid, undecanoicdiacid, sebacic acid, dodecanoic diacid having 9 to 12 carbon atoms.

Particularly, the above-mentioned trimethylhexanoic acid is excellent inreducing solid substances being formed on a surface of the present fluid(hard water stability) when the present fluid (undiluted solution) isdiluted with water.

In view of rot resistance, the alkyl group that is a main chain of thecarboxylic acid preferably has a branched structure. For the carboxylicacid, although dibasic acids are excellent in rust resistance as a salt,dibasic acids and monobasic acids are preferably mixed in use in view ofstability (unlikeliness to be insoluble) of the undiluted solution.

The present fluid may be blended as necessary with publicly-knownvarious kinds of additives as long as such addition is compatible withan object of the present invention. Examples of the additives include anextreme pressure agent, oiliness agent, fungicide (preservative), metaldeactivator and antifoaming agent.

Examples of the extreme pressure agent include a sulfur-based extremepressure agent, a phosphorus-based extreme pressure agent, an extremepressure agent containing sulfur and metal, and an extreme pressureagent containing phosphorus and metal. One of the extreme pressureagents may be used alone or two or more thereof may be used incombination. The extreme pressure agent may be any extreme pressureagent, as long as the extreme pressure agent contains sulfur atoms orphosphorus atoms in its molecule and the extreme pressure agent canprovide load bearing effects and wear resistance. Examples of theextreme pressure agent containing sulfur in its molecule include:sulfurized fat and oil, sulfurized fatty acid, ester sulfide, olefinsulfide, dihydrocarbyl polysulfide, a thiadiazole compound, analkylthiocarbamoyl compound, a triazine compound, a thioterpenecompound, a dialkylthiodipropionate compound and the like. In view ofblending effects, the extreme pressure agent is blended in the undilutedsolution with a content of approximately 0.05 mass % to 0.5 mass % ofthe total amount of the final diluted fluid (coolant).

Examples of the oiliness agent include: an aliphatic compound such asaliphatic alcohol and fatty acid metal salt; and an ester compound suchas polyol ester, sorbitan ester and glyceride. In view of blendingeffects, the oiliness agent is blended in the undiluted solution with acontent of approximately 0.2 mass % to 2 mass % of the total amount ofthe coolant.

The fungicide is exemplified by 2-pyridylthio-l-oxide salt. Examples ofthe fungicide are 2-pyridylthio-l-oxide sodium, zincbis(2-pyridyldithio-1-oxide), and bis(2-sulfidepyridine-1-olato) copper.In view of blending effects, the fungicide is blended in the undilutedsolution with a content of approximately 0.01 mass % to 5 mass % of thetotal amount of the coolant.

Examples of the metal deactivator include benzotriazole, benzotriazolederivative, imidazoline, pyrimidine derivative, and thiadiazole. One ofthe metal deactivator may be used alone or two or more thereof may beused in combination. In view of blending effects, the metal deactivatoris blended in the undiluted solution with a content of approximately0.01 mass % to 3 mass % of the total amount of the coolant.

Examples of the antifoaming agent include methyl silicone oil,fluorosilicone oil, polyacrylates and the like. In view of blendingeffects, the antifoaming agent is blended in the undiluted solution witha content of approximately 0.004 mass % to 0.08 mass % of the totalamount of the coolant.

The water-soluble metalworking fluid according to the above aspect ofthe invention, which is diluted as necessary with water so that itsconcentration is adjusted suitably for the usage, is preferably appliedin various metalworking fields such as grinding, cutting, polishing,squeezing, drawing, flatting and the like. Examples of the grindinginclude cylinder grinding, internal grinding, plane grinding, centerlessgrinding, tool grinding, honing grinding, super finishing, and specialcurve grinding (e.g., screw grinding, gear grinding, cum grinding, androll grinding).

Herein, in the invention, the composition provided by blending thecomponents (A) and (B) means not only a “composition containing thecomponents (A) and (B)” but also a “composition containing a modifiedsubstance of at least one of the components (A) and (B) in place of theat least one of the components (A) and (B), and a “compositioncontaining a reaction product obtained by reacting the component (A)with the component (B)”.

EXAMPLES

Next, the invention will be described in detail with reference toExamples, but is not limited at all by the Examples.

Examples 1 to 5, Comparatives 1 to 6

After water-soluble metalworking fluids (undiluted solutions) wereprepared according to blending compositions shown in Table 1, theundiluted solutions were respectively diluted with tap water by 20 timesin volume to obtain sample oils. The sample oils were subjected to ablock-on-ring test to evaluate lubricity and wear resistance. Testingconditions and evaluation items (evaluation method) are as follows.Results are shown in Table 1.

Block-On-Ring Test

-   -   Test machine: block-on-ring test machine (manufactured by        Marubishi Engineering Co., Ltd.)    -   Load: 100 N    -   Rotation rate: 500 rpm (53 m/min)    -   Time: 10 min    -   Ring: SAE 4620STEEL    -   Block: S45C

Evaluation Items (Evaluation Method)

-   Lubricity    -   Standards of the evaluation based on a friction force (N) are as        follows.    -   A: 13.5 N or less    -   B: more than 13.5 N-   Wear Resistance    -   Standards of the evaluation based on a width of a wear track        (μm) are as follows.    -   A: 1000 μm or less    -   B: more than 1000 μm and 1100 μm or less    -   C: more than 1100 μm

TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Comp. 1 Comp. 2 Comp. 3 Comp. 4Comp. 5 Comp. 6 Blending water 18.7 15.3 15.3 23.4 23.8 61.9 31.9 33.333.3 30.1 23.4 Composition thiodipropionic acid 2.7 2.7 2.7 2.7 2.7 — —2.7 2.7 2.7 2.7 of Stock dodecanoic diacid 1.1 2.0 2.0 2.0 2.0 1.1 1.11.1 1.1 1.1 2.0 Solution decanoic diacid — — — — — 2.0 2.0 — — — — (mass%) 3,5,5-trimethylhexanoic acid 3.2 3.2 3.2 3.2 3.2 3.2 3.2 3.2 3.2 3.23.2 neodecanoic acid (C9) — — — — — 3.4 3.4 3.4 3.4 — — lauric acid(C12) — — — — — — — — — 4.0 — tall oil fatty acid (C18) ¹⁾ 5.4 5.4 5.45.4 5.4 — — — — — 5.4 1-amino-2-propanole 10.0 10.9 10.9 10.9 10.9 8.88.8 10.0 10.0 10.0 10.9 triethanolamine 20.0 21.6 21.6 14.4 14.4 17.517.5 19.4 19.4 20.0 14.4 cyclohexyldiethanolamine — — — 9.1 9.1 — — — —— 9.1 HO(EO)_(8.5)—(PO)_(30.2)—(EO)_(8.5)H ²⁾ — — — 7.5 — — 22.5 15.0 —15.0 15.0 HO(EO)_(13.2)—(PO)₃₀—(EO)_(13.2)H ³⁾ 7.5 7.5 7.5 5.0 5.0 — 7.55.0 5.0 5.0 5.0 MeO(PO)a((EO)b/(PO)c)(PO)Dh ⁴⁾ — — — — 7.5 — — — — — —pentaerythritol polyoxyethylene 22.5 — — — — — — — 15.0 — — ether ⁵⁾pentaerythritol polyoxyethylene — 22.5 — 7.5 7.5 — — — — — — ether ⁶⁾trimethylolpropane — — 22.5 — — — — — — — — tripolyoxyethylene ether ⁷⁾oleyl alcohol 2.0 2.0 2.0 2.0 2.0 — — — — 2.0 2.0 acethylene glycolsurfactant ⁸⁾ 4.8 4.8 4.8 4.8 4.8 — — 4.8 4.8 4.8 4.8 other components⁹⁾ 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 Total 100.0 100.0 100.0100.0 100.4 100.0 100.0 100.0 100.0 100.0 100.0 Evaluation block-on-ringtest: friction 10.8 13.3 13.4 12.3 9.4 21.6 17.3 14.9 13.8 11.8 10.1Results force (N) block-on-ring test: width of 801 846 846 979 991 17231415 1214 1081 1222 1156 wear track (μm) lubricity A A A A A B B B B A Awear resistance A A A A A C C C B C C ¹⁾ Tall Oil Fatty Acid (C18) ²⁾HO(EO)_(8.5)—(PO)_(30.2)—(EO)_(8.5)H: manufactured by Sanyo ChemicalIndustries, Ltd. ³⁾ HO(EO)_(13.2)—(PO)₃₀—(EO)_(13.2)H: manufactured bySanyo Chemical Industries, Ltd. ⁴⁾ CH₃O(PO)a((EO)b/(PO)c)(PO)dH:“BLENBER LUB82” manufactured by Sanyo Chemical Industries, Ltd. ⁵⁾Pentaerythritol polyoxyethylene ether: “PNT-60U” manufactured by NipponNyukazai Co., Ltd. ⁶⁾ Pentaerythritol polyoxyethylene ether: “PNT-40”manufactured by Nippon Nyukazai Co., Ltd. ⁷⁾ Trimethylolpropanetripolyoxyethylene ether: “TMP-60” manufactured by Nippon Nyukazai Co.,Ltd. ⁸⁾ Acethylene glycol surfactant: a mixture of Dynol 604, Surfynol420 and Surfynol 465 which are manufactured by Air Products andChemicals, Inc. ⁹⁾ Other components: 30-mass % aqueous solution ofpolyethyleneimine (molecular weight of 1000) being 0.3 mass %,benzotriazole being 1.0 mass %, 35-mass % aqueous solution ofbenzisothiazoline being 0.2 mass %, sodium pyrithione being 0.2 mass %,and a silicone antifoaming agent being 0.4 mass %

Evaluation Results

As each of coolants obtained by diluting the undiluted solutions ofExamples 1 to 5 contains the components (A) to (D) of the invention, allthe coolants are excellent in lubricity and wear resistance.

In contrast, as each of coolants obtained by diluting the undilutedsolutions of Comparatives 1 to 6 does not contain one of the components(A) to (D), the coolants cannot simultaneously exhibit lubricity andwear resistance.

1. A water-soluble metalworking fluid comprising: a component (A) that is a dicarboxylic acid comprising a sulfide structure; a component (B) that is a polyalkylene glycol; a component (C) that is a polyhydric alcohol polyalkylene oxide adduct; and a component (D) that is a monocarboxylic acid.
 2. The water-soluble metalworking fluid according to claim 1, wherein the component (A) is a compound represented by a formula (1), HOOC—R¹—S_(n)—R²—COOH   (1) where: R¹ and R² are each independently a hydrocarbon group having 1 to 5 carbon atoms, and n is an integer from 1 to
 8. 3. The water-soluble metalworking fluid according to claim 1, wherein a content of the component (A) is in a range from 0.1 mass % to 14 mass %, based on a total amount of the fluid.
 4. The water-soluble metalworking fluid according to claim 1, wherein the component (B) is at least one selected from the group consisting of a compound represented by a formula (2) and a compound represented by a formula (3), HO—(EO)a-(PO)b-(EO)c-H   (2) where: EO denotes an ethylene oxide unit and PO denotes a propylene oxide unit, a and c each independently are an integer from 1 to 30, and b is an integer from 5 to 100, R³O—(R′O)d-H   (3) where: R³ is an alkyl group having 1 to 30 carbon atoms, R′O denotes an oxide unit selected from the group consisting of PO and EO, in which PO and EO are optionally used in mixture, a mole fraction of EO in R′O is less than 1, and d is an integer from 1 to
 50. 5. The water-soluble metalworking fluid according to claim 1, wherein a content of the component (B) is in a range from 10 mass % to 60 mass %, based on a total amount of the fluid.
 6. The water-soluble metalworking fluid according to claim 1, wherein the component (C) is at least one selected from the group consisting of compounds represented by formulae (4) to (7),

where: R¹¹ to R¹⁴ are each independently an alkylene group having 1 to 5 carbon atoms, and e to h are each independently an integer from 1 to 30,

where: R⁴ is an alkyl group having 1 to 30 carbon atoms, R²¹ to R²³ are each independently an alkylene group having 1 to 5 carbon atoms, and i to k are each independently an integer of 1 to 30,

where: R⁵ and R⁶ are each independently an alkyl group having 1 to 30 carbon atoms, R³¹ and R³² are each independently an alkylene group having 1 to 5 carbon atoms, and 1 to m are each independently an integer from 1 to 30,

where: R⁷ to R⁹ are each independently an alkyl group having 1 to 30 carbon atoms, R⁴¹ is an alkylene group having 1 to 5 carbon atoms, and n is an integer from 1 to
 30. 7. The water-soluble metalworking fluid according to claim 1, wherein a content of the component (C) is in a range from 5 mass % to 30 mass %, based on a total amount of the fluid.
 8. The water-soluble metalworking fluid according to claim 1, wherein the component (D) is a compound represented by a formula (8), R¹⁰—COOH   (8) where: R¹⁰ is a hydrocarbon group having 11 or more carbon atoms.
 9. The water-soluble metalworking fluid according to claim 1, wherein a content of the component (D) is in a range from 1 mass % to 20 mass %, based on a total amount of the fluid.
 10. The water-soluble metalworking fluid according to claim 1, further comprising: a component (E) that is an acetylene glycol surfactant.
 11. The water-soluble metalworking fluid according to claim 10, wherein the component (E) is an acetylene glycol ethylene oxide adduct.
 12. The water-soluble metalworking fluid according to claim 10, wherein a content of the component (E) is in a range from 1 mass % to 15 mass %, based on a of the total amount of the fluid.
 13. The water-based metalworking fluid according to claim 1, wherein the water-based metalworking fluid is in a form of an undiluted solution comprising water in a range from 15 mass % to 75 mass %.
 14. A metalworking coolant obtained by diluting the water-based metalworking fluid according to claim 1 with water by 2 to 200 times in volume.
 15. The metalworking coolant according to claim 14, wherein the metalworking coolant is suitable for use in grinding. 